In recent years, with advancement of miniaturization, a write speed of a NAND type flash memory is reduced. On the other hand, since an amount of data processed by a memory system having NAND type flash memories tends to increase, improvement in the write performance of the memory system is attempted by executing a write operation with respect to the NAND type flash memories at the same time.
In this case, however, since the NAND type flash memories are operated at the same time, an operation current is increased. In particular, there is a concern that peaks of the operation currents in the NAND type flash memories overlap and a large peak current flows.